In the rice milling industry, whole grain yield is highly valued. A broken grain is worth half or less in the marketplace compared to a whole grain. Also, a small difference in the amount of broken grains level in the milled rice will significantly lower its quality grade. As such, broken grains are removed from milled rice and sold off at a lower price.
The milling industry consists of two general types of rice mills: white rice mills and parboiled rice mills. In a white rice mill the rough rice is dehulled and milled, along with numerous mechanical cleaning and defect separation operations. In a parboiled rice mill, the rough rice is steeped in hot water, steamed, dried, dehulled and milled, along with numerous mechanical cleaning and defect removal operations. Parboiling has several advantages for improving the rice's cooking quality and milling yield.
For a white rice miller, brokens in milled rice are in part caused by imperfect grain structure. These are immature grains, chalky grains and internally cracked grains in rough rice. Immature grains are underdeveloped, are generally thin and break easily. Chalky grains have milk-white or opaque centers and are sometimes called white bellies. Chalkiness is caused by the presence of air or due to less dense packing of starch in the endosperm. It is soft and also breaks easily. Cracked kernels are caused by either over drying prior to harvest, uncontrolled moisture adsorption or desorption, mechanical harvest damage, or by some other post harvest damage. Rapid or uncontrolled moisture change causes mechanical stress in the rice kernel. If the stress exceeds the tensile strength of the kernel, a crack or check is the result. For parboiled rice millers, neither chalk nor cracked grains cause breakage as they are almost completely healed during the hydro-thermic processing. Thus, parboiled rice millers have a whole kernel yield advantage over white rice millers. This disadvantage could be eliminated, if the white rice millers could obtain crack and chalk free rice for milling.
The following disclosures are related to the sorting process used in the present invention. Massen, et al., U.S. Pat. No. 5,524,746, discloses an apparatus for sorting bulk rice using an optical monitor to detect grains of different color or luminosity or grains of different size or shape that travel on a conveyor belt. When the optical monitor detects an imperfect rice grain, a jet of air from a nozzle removes the grain from the conveyor belt. Satake, et al., U.S. Pat. No. 5,245,188, discloses an apparatus for evaluating the grade of rice grains using grooved chutes in which the individual grains fall through past a light source. Detectors measure both the reflected and transmitted light from each grain and determine if the grain is complete, scratched or discolored. Inferior grains are sucked from the grooved chutes and removed through a different outlet. Satake, U.S. Pat. No. 4,806,764, discloses an apparatus for evaluating the quality of rice grains using an infrared spectrometer with a band-pass filter and detectors for measuring reflected light to measure the content percentages of pre-selected constituents, such as protein, amylose, amylopectin, and moisture. From the various content percentages, quality evaluation values are determined. Satake, U.S. Pat. No. 4,752,689, is related to the previous patent except that it prints or displays the actual percentage contents of constituents. Gillespie, et al., U.S. Pat. No. 4,666,045, discloses a pit detection apparatus and method for fruit sorting using a sweeping transmission scanning beam with sensors and a sizing beam with sensors. Pits are detected from analyzing the amount of light transmitted through the fruit at various points in the fruit. Fruit with pits are then removed by an ejector valve. Satake, U.S. Pat. No. 4,572,666, discloses an apparatus for detecting cracked rice grains in hulled or unhulled grains using a chute or conveyor belt, a light source, and two light detectors. Cracked grains are determined by comparing the amount of light transmitted through leading half part of an inspected grain to its trailing half part. Based on the grain's position, less light will be transmitted through one-half of a cracked grain in comparison to the other half. Pilesi, et al., U.S. Pat. No. 4,196,811, sorts buttons by measuring the amount of light transmitted through each button as it travels down a chute. Murata, U.S. Pat. No. 3,871,774, detects cracks in unhulled grains by irradiating the grain with a laser and measuring the light transmitted through the grain which is conveyed through the laser beam. The amount of light transmitted through the grain decreases when a crack is scanned. The patent does not disclose a method to sort the grains, a laser line, a means to separate grains for detection, a grain stabilizing means, or any features to make the invention commercially efficient. Fraenkel, U.S. Pat. No. 3,197,647, sorts white from red rice by measuring the light transmitted through each grain. Twamley, U.S. Pat. No. 1,031,669, tests the maturity of corn kernels by transmitting light through the kernels. Brizgis, et al., U.S. Pat. No. 4,713,781, analyzes damaged grain by illuminating a grain with long wave, ultraviolet radiation, causing the exposed starch of the damaged section to fluoresce. The amount of fluoresce determines the amount of damage to the grain.
With the conventional apparatus or methods disclosed above, it is not possible to sort internally cracked unhulled grains from internally whole unhulled grains in a commercially efficient manner for use by rice millers. For commercial purposes, the evaluation of unhulled grains must be done quickly with minimum error. In the previously disclosed art, a rice grain travelling at a high velocity may not be properly stabilized when it is analyzed because air resistance and other factors may oppose the natural grain orientation. If the grain is wobbling, a structural defect may not be detected. The prior art also does not disclose adequate methods for separating each grain prior to analysis. Additionally, the lasers used to analyze objects in the previously disclosed art are typically focused to the smallest spot size possible and do not illuminate some defects that are not precisely positioned. Also, the photo detection systems used do not provide a strong signal for better resolution of the signal. With a commercially efficient sorting invention, unhulled rice could be separated into two fractions: internally whole and internally defective unhulled grains. Then, white rice millers could process the internally whole unhulled grains for a higher yield and would pay a premium price for the internally whole unhulled grain. The internally defective unhulled grains--which would have resulted in broken rice for the white rice millers--can be used by parboilers for processing.